Condenser microphone



May 13, 1930. F. c. BARTON CONDENSER MICROPHONE Filed June 18, 1928 Inventor:

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aan@ ay is, 193e ATENT OFFICE FREDERICK C. BARTON, 0F SCH'ENECTADY, NEW YORK, ASSIGNOR TO GENERAL- ELEC- TRIC COMPANY, A CORPORATION OF YORK CONDENSER MICROPHONE Application filed .Tune 18,

My invention relates to condenser microphones capable of having their capacity varied in accordance with sound vibrations, and has for its principal object an improved construction whereby the capacity of such condensers is maintained substantially independent of atmospheric conditions.

Microphones of the'electrostatic type are preferably provided with a metal diaphragm constituting one plate of the condenser and adapted kto vibrate in accordance with sound vibrations impinging thereon. This diaphragm is properly stretched and supported so that it is insulated and separated from a second rigid plate by an enclosed space containinga dielectric which is preferably air. For the eiiicient operation of this type of condenser it is desirable to maintain the diaphragm independent of atmospheric pressure variations and to maintain the dielectric independent of humidity variations. i

In accordance with my invention a chamber partly enclosed by a yielding member such as a rubber diaphragm is interconnected with the dielectric chamber between the condenser plates. This arrangement permits maintaining the pressure of the dielectric therein in accordance with atmospheric pressure exerted upon the yielding member so that the atmospheric and dielectric pressures on the two sides of the metallic diaphragm respectively, are substantially equal.

The novel features which- I believe to be characteristic of my invention'are pointed out in the appended claims. My invention itself, however, will best be understood by reference to the accompanying drawing in which 1 illustrates a front view of a condenser microphone constructed in accordance with my invention; Fig. 2 is a sectional view thereof looking in the direction of arrow A; Fig. 3 is an enlarged section of Fig. 2; and Fig. 4 is an exploded view of Fig. 3.

Referring to the drawing in detail, 10 is a metal diaphragm, preferably of a light `metal alloy, which is clamped between two collars 11 and 12, the adjoining surfaces 13 and 14 of which are provided with a plurality of successive sinusoidal grooves and ridges. It is important, for'the proper operation of 192s. serial No. 286,197.

the diaphragm, that :it be uniformly clamped with substantially no deformation. The sinusoidal grooves and ridges provide a maximum of clamping surface with thc least possible deformation and with the use of paper washers 15 and 16 an additional protection of the clamped surfaces is obtained. Subsequent to the clamping, the diaphragm is stretched by forcing ring 17 against its surface with the aid of threaded ring 25.

In the assembled apparatus, a washer 2l is placed inside the collar 11 and a member 20, having its surface inline with the surface of electrode 19, is rmly held against it by suitable clamping means. The electrode 19 is, therefore, spaced from the diaphragm by a distance determined by the thickness of outer surface exposed to the atmosphere seals the dielectric from the surrounding air but allows it to expand and contract in accordance with temperature changes and maintains it under a pressure substantially equal to that of the surrounding atmosphere. The electrodes are connected to a suitable source of energy by`y conductors attached to screws 26 and 27 respectively'. l

In the operation of the microphone, a suitable difference of electric potential is maintained between the electrodes and when sound waves vibrate the diaphragm the spacing between the electrodes, and consequently the capacity, varies iny accordance with these vibrations. The capacity variations, or impulses, are impressed upon suitable amplifying. and transmitting apparatus and may be eventually reconverted into sound.

l l .2 K 1,758,777

What I claim as new and desire to secure I by Letters Patent of the United States, is,-

1. In a condenser microphone, a diaphragm, means for clamping said diaphragm e l including clamping surfaces comprising a plurality of successive sinusoidal grooves and ridges arranged to overlapthe edge of said diaphragm, non-metallic rings'interposed between said diaphragm and said surfaces and 1o means arranged to force said surfaces toward each other.

2. 'In a condenser microphone, a diap phragm, means for clampingfsaiddiaphragm yincluding a pair of rings provided( with 15 clamping surfaces comprising a plurality of successive sinusoidal grooves and ridges arranged parallel to each other, insulating rings interposed between said diaphragm and said surfaces, means arranged to force said sur- 20 faces toward leach other, and a movable member arranged Within one of said rings to be forcedL against said diaphragm. In Witnessy whereof, I have hereunto set my hand this 15th da of June, 1928. v g5 FRElgERICK C. BARTON. 

